I. Field of the Invention
The present invention generally relates to a wireless information storage device and a method for putting a wireless information storage device on or into an article. More particularly, the present invention relates to a device and a method for achieving both certainty and efficiency of a plurality of wireless information storage devices being communicated by a reader/writer system at a time.
II. Background and Material Information
A wireless information storage device, such as a wireless card or a wireless tag, has recently attracted a great deal of attention as an internal information carrier of the next generation because of its capability to read and write information with an external reader/writer system while being not being connected to the external system.
The wireless information storage device comprises a loop-shaped coil antenna that transmits signals to and receives signals from a wireless transmitter/receiver via wireless communication. The wireless transmitter/receiver comprises a large scale integrated circuit (LSI) and a memory for storing information. The wireless transmitter/receiver generates information, such as read, write, or command data, by demodulating a signal received via a coil antenna. The wireless transmitter/receiver also generates a signal to be transmitted via the coil antenna by modulating information. Both the antenna and the wireless transmitter/receiver may be molded in a plastic case hereinafter referred to as “molded case.”
A multi-reader/writer system is used to communicate with the wireless information storage device. The multi-reader/writer system communicates with a plurality of wireless storage devices using single antenna. However, to effectively communicate, the multi-reader/writer system requires that the wireless information storage devices are not perfectly stacked, and thus not aligned so that the system could process information unerringly.
That is, if every molded case to be communicated with at a time has a same shape, and also has a same shaped built-in coil antenna in the same position, a ‘coupling coil’ that is composed of all the aligned coil antennas is created. The coupling coil causes a shift of the resonance point of each wireless information storage device. Furthermore, as the number of wireless information storage devices perfectly stacked increases, an electromotive force generated in the coil antenna of each of the wireless information storage devices is weakened because a magnetic flux going through the coil antenna is weakened.
Thus, when a plurality of wireless information storage devices is perfectly stacked, the multi-reader/writer system can not process information unerringly. Therefore, the efficiency for processing information for each wireless information storage device is low.
Furthermore, in case that each of a plurality of wireless information storage devices is located at the same position of an item, such as a compact disc (CD), to be communicated at a time, the efficiency for processing information for each item is low by the same reason.